If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
There is no reason that your probe should not work well when measuring a DC voltage, such as is present on a correctly functioning CW multiplier.
From this you can conclude that either your multiplier is not working properly (and it outputting a large AC component), or that you are getting some type of internal corona/sparking loss in your probe.
One experiment to try-connect a capacitor across the output of the CW (if you have access to doorknob caps a few in series would work well, if not you may need to resort to something like a glass parallel plate capacitor of a few nf) and charge it up with the CW. You can then be sure that the output is a pure DC, and your measurements will be correct.
Furthermore, while it is sketchy business connecting a 1Gohm resistor directly in series with a voltmeter, there is no reason that the impedance of your voltmeter should vary significantly from 1Mohm. Most digital voltmeters internally have a very high input impedance (into the Gohm range), and have a resistor in parallel with the output so that stray charge does not cause false readings--and to insure the meter has a constant known input impedance for applications such as this. If you want to be sure, measure the input impedance using your nice voltmeter, you should find it reads quite close to 1Mohm. The neon bulb across the input is a good idea, as is making sure that you have the other side of the bulb well grounded to something that is known to be ground--not simply the negative of a power supply/voltmeter.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
+1, except that DMMs don't have a constant known input impedance. It's not unknown for it to vary with the range. If it does then it's usually extremely high (100M? 1G? Not sure) on the lowest DC voltage range and 11M Ohms on all the higher ones.
So, if your meter is autoranging while it's connected to the divider, the autoranging could go unstable. I would lock the meter to the 10V range and put a 1M resistor across it, to be sure.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Although wirewound resistors do have inductance I doubt that it will be significant. i.e. at what frequency will the inductive reactance be 1% of Rdc ? (L=(r.n)squared/(9r+10h) etc.) The 100 MOhm resistor in my p6015 is one long helix. In low-voltage high-current circuits the inductance of wirewound resistors (or even wires) can be very significant. For a large C-W/Greinacher I would use a moving coil meter with a couple of 1N4148 and a capacitor across it and a string of resistors. For a small C-W the 50uA may be too much of a load. Tap off one of the resistors a Gas Discharge Tube of the type used for telephone lines to a reliable 'earth'. It's quite difficult to be completely safe at the end of a resistor string from eht. and dmms are very susceptible to emi/rfi.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Sulaiman wrote ...
Although wirewound resistors do have inductance I doubt that it will be significant. i.e. at what frequency will the inductive reactance be 1% of Rdc ? (L=(r.n)squared/(9r+10h) etc.) The 100 MOhm resistor in my p6015 is one long helix. In low-voltage high-current circuits the inductance of wirewound resistors (or even wires) can be very significant. For a large C-W/Greinacher I would use a moving coil meter with a couple of 1N4148 and a capacitor across it and a string of resistors. For a small C-W the 50uA may be too much of a load. Tap off one of the resistors a Gas Discharge Tube of the type used for telephone lines to a reliable 'earth'. It's quite difficult to be completely safe at the end of a resistor string from eht.
Agreed.
Sulaiman wrote ...
and dmms are very susceptible to emi/rfi.
yes, mine have gone entirely erratic due to rfi and emi, that which is not conductivly connected, ONLY RADIATED across near distances!!
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
Patrick wrote ...
yep, thats my plan.
How about using Nichrome wire? The precision of the resistors isn't very important, it's cheap and no need to worry about dielectric strength of the resistor housing.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Pinky's Brain wrote ...
Patrick wrote ...
yep, thats my plan.
How about using Nichrome wire? The precision of the resistors isn't very important, it's cheap and no need to worry about dielectric strength of the resistor housing.
They put resistors in a capacitive voltage divider to damp the oscillations from self inductance (it's for very high voltages where the voltage gradients along the divider have to be air compatible).
Similar to the Glassman divider, except they tuned it for low bandwidth and put a high resistance resistor across the pair for DC balancing.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
i read that atricle but failed to realise what you meant, but i think the lenth of 50 + miles and TCo would be difficult to work around. but ill look at the math again.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
DIY High voltage probe
